1. Field of the invention
This invention relates in general to subsea well drilling, and in particular to a split wear bushing that holds the drill pipe away from the casing near the casing hanger to avoid key seating.
2. Description of the Prior Art
In subsea well drilling of the type concerned herein, a wellhead housing will be located at the sea floor. After the well has been drilled to a selected depth, casing will be lowered into the well and cemented into place. A casing hanger lands at the wellhead housing, the casing hanger being secured by threads to the upper end of the casing. Then, the operator will lower a drill bit from the drilling vessel down through the wellhead housing into the well for further drilling.
Damage can occur to the casing hanger bore and casing by the contact of rotating drill pipe while drilling. This can particularly be a problem when the drill pipe has hardened or otherwise enhanced wear resistant tool joints. It is possible for the drill pipe to wear a hole into the casing from the rubbing contact during drilling.
Wear bushings are normally employed to prevent damage to the casing hanger. A typical wear bushing is a tubular member that lowers into and seats in the casing hanger. A typical prior art wear bushing has a bore that is the same as the bore of the lower section of the casing hanger and the same as the inner diameter of the casing. Although prior art wear bushings will protect the casing hanger from damage, they do not have a means to prevent damage to the casing near the point where the casing secures to the casing hanger.